1. Field of the Invention
The present invention relates to a solid-state image sensing device and a method for manufacturing a solid-state image sensing device.
2. Description of the Related Art
In recent years, a solid-state image sensing device has been miniaturized and its pixel becomes increasingly densified, with which a light receiving area is reduced and a deterioration of characteristics such as a drop of the sensitivity or the like is caused.
It has been proposed as measures against the drop of sensitivity to promote a light collecting efficiency on to a light receiving sensor unit by providing, e.g. a microlens, that is called an on-chip lens and an intra-layer lens.
A structure of the conventional solid-state image sensing device will be described below.
FIG. 1 shows a schematic sectional view of a conventional solid-state image sensing device 100 in the solid-state image sensing device with a structure having an intra-layer lens.
As shown in FIG. 1, a large number of light receiving sensor units 102 for performing the photoelectric conversion are formed in an array on a silicon substrate 101.
On one side of the light receiving sensor unit 102 is formed a charge transfer element 104 through a readout gate 103. On the other side thereof is formed a charge transfer element 104 to the other light receiving sensor unit 102 through a channel stop 105.
A signal charge derived from the photoelectric conversion by the light receiving sensor unit 102 is read out to the one charge transfer element 104 through the readout gate 103 and further transferred by the charge transfer element 104.
Moreover, on the surface of the silicon substrate 101 is provided a SiO.sub.2 insulator film 106 formed by the thermal oxidation method or CVD (Chemical Vapor Deposition) method, and so forth.
On the insulator film 106 nearly just above the charge transfer element 104 is formed a transfer electrode 107 made of polysilicon, and besides another transfer electrode (not shown) is formed in such a manner as partially overlapped with the transfer electrode 107.
On the surface of these transfer electrodes 107, i.e. on the top surface and the side surface thereof is formed, an interlayer insulator film 108 which covers the transfer electrode 107 and further covers the insulator film 106 on the light receiving sensor unit 102 facing between the transfer electrodes 107.
On the interlayer insulator film 108 is formed a light shielding film 109 which covers the transfer electrode 107. The light shielding film 109 has an overhang portion 109a which projects just over the light receiving sensor unit 102 in order to restrict a smear. An opening 110 is formed just over the light receiving sensor unit 102 in such a manner as surrounded by the overhang portion 109a. In addition, the light shielding film 109 is formed by a metal of high melting point, e.g. tungsten.
On the light shielding film 109 is formed an interlayer film 111 made of BPSG (boron phosphorus silicate glass), which covers the light shielding film 109 and the interlayer insulator film 108 facing the opening 110. The interlayer film 111 is subjected to the reflow processing in order to form a recess 111a formed on the light receiving sensor unit 102 between the transfer electrodes 107. This recess 111a is processed to be adjusted to have a required curvature.
On this interlayer film 111 is formed a passivation film 112 covering its surface.
The recess 111a of the interlayer film 111 is filled by an intra-layer lens material which forms an intra-layer lens 114 over the passivation film 112, the lens having a protuberance with the required curvature in accordance with the recess 111a.
This intra-layer lens 114 is made flat of its surface by the known so-called resist etch back process or the CMP process (chemo-mechanical polishing process).
On the flattened intra-layer lens 114 is formed a color filter layer 116. This color filter layer 116 can be formed by a known process using such resin, and so forth. into which a pigment is dispersed.
On the color filter layer 116 is formed a microlens 117 made of a transparent resin and the like. The microlens 117 directs an incident light to the opening 109a of the light shielding film 109 through the intra-layer lens 114 so that the light may be incident onto the light receiving sensor unit 102. Therefore, the curvature of the microlens 117 is chosen to have a desired value depending on a distance from the light receiving sensor unit 102 to the bottom plane of the microlens 117 in the solid-state image sensing device 100 shown in FIG. 1.
However, the solid-state image sensing device with the arrangement shown in FIG. 1 causes the following inconvenience.
Specifically, because the solid-state image sensing device 100 having the structure including the intra-layer lens 114 shown in FIG. 1 is provided with the intra-layer lens 114 and the color filter layer 116 respectively, an overall thickness from the light receiving sensor unit 102 to the bottom plane of the microlens 117 reaches the extent of 4 to 5 .mu.m or more. This means that there is a large distance between the light receiving sensor unit 102 and the microlens 117.
When the distance from the light receiving sensor unit 102 to the microlens 117 becomes large in this manner, in the case where an incident light inclined relative to the microlens 117 increases, if the diaphragm of an image sensing lens of camera is opened as shown in FIG. 2, the light collected by the microlens 117 will deviate from the center of the opening of the light shielding film 109 as shown by broken lines in FIG. 2, thereby causing a rate of collecting the light onto the light receiving sensor unit 102 to be lowered. In other words, the dependence on F value goes worse and so the sensitivity to the parallel light is satisfactory, whereas the sensitivity drops remarkably toward the diaphragm being opened. Moreover, when the collected light approaches an opening end of the light shielding film 109, a signal charge is caused to be mixed in the adjacent light receiving sensor unit 102 or charge transfer area (not shown), thus making what is called a smear to occur.
Furthermore, because the curvature of the microlens 117 is determined depending on the distance from the light receiving sensor unit 102 to the microlens 117 as described above, when the distance from the light receiving sensor unit 102 to the microlens 117 increases, it will be necessary to make larger the curvature of the microlens accordingly.
When the curvature of the microlens 117 on the color filter 116 becomes large in this manner, a light L collected by the microlens 117 is rejected by an edge of the color filter 116, as shown in FIG. 1. This effects an increase of minute black spots, this causing the deterioration of picture quality.